The input/output scan is emulated using subroutine
I O Scan. There, the 8 bit input port (fig. 5) is read and the status of
the individual bits stored in the input table. Also the status of the
output points from the output table is written to the 8 bit output port (see fig. 6). The Progr~ Scan
subroutine is a direct translation of the ladder diagram in fig. 4. For every rung in the ladder logic there is
an if-then-else statement. The Initialize and Finalize subroutines were added to handle the state of the
output points and internal relays during the startup and shutdown of the PLC program.